Modular rod reduction tower and related methods

ABSTRACT

A bone fixation system includes a bone fastener and a tower including a detachable distal section with a thread formed on an inner surface thereof, the tower having at least one flexible section and at least one rigid section to accommodate and/or mitigate tower interference and/or collision. The distal section can be detached from the tower to function as a head locking unit of the bone fixation assembly, with the detached distal section capable of accommodating set screws, fixation rods and/or other spinal hardware.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of Utility patent applicationSer. No. 15/335,026 filed Oct. 26, 2016, titled “Modular Rod ReductionTower and Related Methods,” which claims priority to and benefit thereoffrom U.S. Provisional Patent Application No. 62/247,183 filed Oct. 27,2015, titled “MODULAR DEROTATION TOWER WITH ROD REDUCTION SLEEVE,” andU.S. Provisional Patent Application No. 62/257,124, filed Nov. 18, 2015,titled “MODULAR ROD REDUCTION TOWER WITH THREAD PITCH COMPENSATIONFEATURE AND METHODS OF USE,” all of which are hereby incorporated hereinby reference in their entireties.

This application further claims priority to and the benefit of U.S.Provisional Patent Application No. 62/758,120 filed Nov. 9, 2018, titled“Flexible MIS Tower,” which is also hereby incorporated herein byreference in its entirety.

FIELD OF THE DISCLOSURE

The present disclosure relates to a bone stabilization system andmethod, and more particularly to a bone stabilization system and methodfor implanting within a body of a patient.

BACKGROUND OF THE DISCLOSURE

In mammals, the spinal (or vertebral) column is one of the mostimportant parts. The spinal column provides the main support necessaryfor mammals to stand, bend, and twist.

In humans, the spinal column is generally formed by individualinterlocking vertebrae, which are classified into five segments,including (from head to tail) a cervical segment (vertebrae CI-C7), athoracic segment (vertebrae TI-TI2), a lumbar segment (vertebrae LI-L5),a sacrum segment (vertebrae SI-S5), and coccyx segment (vertebrateCol-CoS). The cervical segment forms the neck, supports the head andneck, and allows for nodding, shaking and other movements of the head.The thoracic segment attaches to ribs to form the ribcage. The lumbarsegment carries most of the weight of the upper body and provides astable center of gravity during movement. The sacrum and coccyx make upthe back walls of the pelvis.

Intervertebral discs are located between each of the movable vertebra.Each intervertebral disc typically includes a thick outer layer calledthe disc annulus, which includes a crisscrossing fibrous structure, anda disc nucleus, which is a soft gel-like structure located at the centerof the disc. The intervertebral discs function to absorb force and allowfor pivotal movement of adjacent vertebra with respect to each other.

In the vertebral column, the vertebrae increase in size as they progressfrom the cervical segment to the sacrum segment, becoming smaller in thecoccyx. At maturity, the five sacral vertebrae typically fuse into onelarge bone, the sacrum, with no intervertebral discs. The last three tofive coccygeal vertebrae (typically four) form the coccyx (or tailbone).Like the sacrum, the coccyx does not have any intervertebral discs.

Each vertebra is an irregular bone that varies in size according to itsplacement in the spinal column, spinal loading, posture and pathology.While the basic configuration of vertebrae varies, every vertebra has abody that consists of a large anterior middle portion called the centrumand a posterior vertebral arch called the neural arch. The upper andlower surfaces of the vertebra body give attachment to intervertebraldiscs. The posterior part of a vertebra forms a vertebral arch thattypically consists of two pedicles, two laminae, and seven processes.The laminae give attachment to the ligament flava, and the pedicles havea shape that forms vertebral notches to form the intervertebral foraminawhen the vertebrae articulate. The foramina are the entry and exitpassageways for spinal nerves. The body of the vertebra and the verticalarch form the vertebral foramen, which is a large, central opening thataccommodates the spinal canal that encloses and protects the spinalcord.

The body of each vertebra is composed of cancellous bone that is coveredby a thin coating of cortical bone. The cancellous bone is a spongy typeof osseous tissue, and the cortical bone is a hard and dense type ofosseous tissue. The vertebral arch and processes have thicker coveringsof cortical bone.

The upper and lower surfaces of the vertebra body are flattened andrough. These surfaces are the vertebral endplates that are in directcontact with the intervertebral discs. The endplates are formed from athickened layer of cancellous bone, with the top layer being denser. Theendplates contain adjacent discs and evenly spread applied loads. Theend plates also provide anchorage for the collagen fibers of the disc.

FIG. 1 shows a portion of a patient's spinal column 2, includingvertebra 4 and intervertebral discs 6. Each disc 6 forms afibrocartilaginous joint between adjacent vertebrae 4, allowing relativemovement between adjacent vertebrae 4. Beyond enabling relative motionbetween adjacent vertebrae 4, each disc 6 acts as a shock absorber forthe spinal column 2.

As noted earlier, each disc 6 comprises a fibrous exterior surroundingan inner gel-like center which cooperate to distribute pressure evenlyacross each disc 6, thereby preventing the development of stressconcentrations that might otherwise damage and/or impair vertebrae 4 ofspinal column 2. Discs 6 are, however, subject to various injuriesand/or disorders which may interfere with a disc's ability to adequatelydistribute pressure and protect vertebrae 4. For example, discherniation, degeneration, and infection of discs 6 may result ininsufficient disc thickness and/or support to absorb and/or distributeforces imparted to spinal column 2. Disc degeneration, for example, mayresult when the inner gel-like center begins to dehydrate, which mayresult in a degenerated disc 8 having decreased thickness. Thisdecreased thickness may limit the ability of degenerated disc 8 toabsorb shock which, if left untreated, may result in pain and/orvertebral injury.

Thus, when a spinal abnormality occurs, the abnormality can cause severepain or damage to the nervous system. The abnormality may also severelylimit movement of the spinal column. The abnormality may be the resultof, for example, trauma, degenerative disc disease, degenerative bonedisease, or the like.

There exists an unfulfilled need for improved bone stabilizationdevices, associated systems, and methodologies related thereto. Sincerecovery from spinal surgery is typically a long and arduous processthat places severe restrictions on patient mobility, a continuing needexists for systems and methodologies that improve patient recovery andreduce recovery time after surgery.

SUMMARY OF THE DISCLOSURE

According to an aspect of the disclosure, a bone fixation systemincludes a bone fastener, a tower including a first thread formed on aninner surface at a first end thereof, a coupling assembly connected tothe bone fastener and the first end of the tower. The coupling assemblyincludes a coupling unit including a second thread formed on an innersurface at an upper portion thereof and adjoining the first thread, anda set screw including a third thread configured to mate with the firstthread and the second thread. The coupling unit is configured tocompensate a thread pitch mismatch between the first thread and thesecond thread.

The bone fastener includes a polyaxial pedicle screw having a head and ascrew shaft extending from the head.

The coupling assembly further includes a cavity that receives and holdsa portion of the bone fastener.

The coupling assembly further includes a channel formed by a pair ofupper inner walls of the coupling unit.

The bone fixation device further includes a fastener connector having aportion that seats within the channel.

The tower further includes a coupling guide formed around an innersurface at the first end portion thereof.

The coupling unit further includes a coupling lip formed on an outersurface of an upper portion thereof that seats in the coupling guide ofthe tower.

The coupling guide is formed by a recessed surface extending between anupper recess surface and a lower recess surface, the recess surfacebeing wider than the coupling lip of the coupling unit.

The coupling unit travels in a direction in response to a force appliedby the set screw when the first thread and the second thread aremisaligned.

The third thread of the set screw mates with the second thread of thecoupling unit when a thread pitch of the first thread is aligned with athread pitch of the second thread.

According to another aspect of the disclosure, a bone fixation systemincludes a tower having a tower body that includes an internal towerthread, and a thread pitch compensator. The thread pitch compensatorsubstantially matches the pitch of the tower thread to a pitch of athread in a coupling body to facilitate progression of a set screw fromthe tower thread into and along the thread in the coupling body.

The thread pitch compensator includes a coupling guide that holds andguides a coupling lip on the coupling body.

The thread pitch compensator includes a tower lip.

The thread pitch compensator includes a stop that limits travel of thecoupling lip in the coupling guide.

The coupling guide allows the coupling lip to move in either directionalong a longitudinal axis of the tower.

According to yet another aspect of the disclosure, a bone fixationsystem includes a hollow shell body having an opening at a first endportion thereof, and a derotation tower that envelopes a tower of a bonefastener when inserted into the hollow shell body via the opening of thehollow shell body.

The hollow shell body includes a grip portion having a diameter greaterthan that of the first end portion thereof.

The bone fixation system further includes a crosslink unit thatremovably affixes to a second end portion of the hollow shell body.

A length of the crosslink unit is adjustable.

The crosslink unit includes a bent end portion that removably affixes tothe second end portion of the hollow shell body.

Additional features, advantages, and embodiments of the disclosure maybe set forth or apparent from consideration of the detailed descriptionand drawings. Moreover, it is to be understood that both the foregoingsummary of the disclosure and the following detailed description areexemplary and intended to provide further explanation without limitingthe scope of the disclosure as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the disclosure, are incorporated in and constitute apart of this specification, illustrate embodiments of the disclosure andtogether with the detailed description serve to help explain theprinciples of the disclosure. No attempt is made to show structuraldetails of the disclosure in more detail than may be necessary for afundamental understanding of the disclosure and the various ways inwhich it may be practiced. In the drawings:

FIG. 1 illustrates a portion of a patient's spinal column;

FIG. 2 shows an example of a bone fixation system that may be implantedin a spinal column, according to the principles of the disclosure;

FIG. 3A shows an example of a bone fixation device, constructedaccording to the principles of the disclosure;

FIGS. 3B and 3C show enlarged views of portions of the bone fixationdevice in FIG. 3A;

FIG. 3D shows an enlarged cross-section cut view of an example of athread pitch compensation feature in a bone fixation device, accordingto the principles of the disclosure;

FIG. 3E shows a bottom view of an example of a tower, constructedaccording to principles of the disclosure;

FIGS. 4A, 4B and 4C show enlarged views of a connection portion of thebone fixation system in FIG. 3A;

FIG. 5 shows an example of a derotation device, constructed according tothe principles of the disclosure;

FIG. 6A shows the derotation device in FIG. 5 and a derotation toweraccording to the principles of the disclosure;

FIG. 6B shows the derotation device encapsulating the derotation towerin FIG. 6A;

FIG. 7 shows an example of a bone fixation system, including a crosslinkfor linking two or more derotation devices to each other, according tothe principles of the disclosure;

FIG. 8A depicts an exemplary embodiment of tower bodies that incorporateone or more flexible portions;

FIG. 8B depicts an alternative embodiment of tower bodies thatincorporate one or more flexible portions, including a modular towerincorporating a removable and/or reconfigurable flexible section;

FIG. 9A depicts an exemplary interference or collision of tower bodiesin a spine analog;

FIG. 9B depicts a correctly aligned fixation construct with set screwtightened;

FIG. 9C depicts a misaligned fixation construct with set screwtightened;

FIGS. 10A and 10B depict attachment of a spinal instrument having aflexible zone being attaching to a spinal fixation element;

FIGS. 11A and 11B depict another embodiment of a percutaneous spinalinstrument having flexible zones in accordance with the presentdisclosure;

FIGS. 12A through 12C and 13A through 13F depict additional alternativeembodiments of flexible regions that can be integrated into variousspinal instrumentation;

FIGS. 14A through 14C depict additional alternative embodiments offlexible towers;

FIGS. 15A through 15D depict an additional embodiment of a tower bodythat includes a tubular body portion with an integrated detachable tipportion;

FIGS. 16A through 16C depict another alternative embodiment of a towerbody with an integrated detachable tip portion;

FIG. 17 depicts one exemplary method of removing a tubular body portionfrom a tip portion of a tower body;

FIGS. 18A and 18B depict front plan and cross-sectional views,respectively, of one embodiment of an exemplary fixation elementincorporating a tip portion which engages with a bone fastener in theform of a polyaxial pedicle screw; and

FIG. 19A through 19D depict various views of a set screw for use withvarious embodiments of the present invention.

The present disclosure is further described in the detailed descriptionthat follows.

DETAILED DESCRIPTION OF THE DISCLOSURE

The disclosure and the various features and advantageous details thereofare explained more fully with reference to the non-limiting embodimentsand examples that are described and/or illustrated in the accompanyingdrawings and detailed in the following description. It should be notedthat the features illustrated in the drawings are not necessarily drawnto scale, and features of one embodiment may be employed with otherembodiments as the skilled artisan would recognize, even if notexplicitly stated herein. Descriptions of well-known components andprocessing techniques may be omitted so as to not unnecessarily obscurethe embodiments of the disclosure. The examples used herein are intendedmerely to facilitate an understanding of ways in which the disclosuremay be practiced and to further enable those of skill in the art topractice the embodiments of the disclosure. Accordingly, the examplesand embodiments herein should not be construed as limiting the scope ofthe disclosure. Moreover, it is noted that like reference numeralsrepresent similar parts throughout the several views of the drawings.

Referring to FIG. 1, when a spinal abnormality occurs in the spinalcolumn 2, the abnormality can cause severe pain or damage to the nervoussystem, and the abnormality may limit movement of the spinal column. Asnoted earlier, the abnormality may be the result of, for example,trauma, degenerative disc disease, degenerative bone disease, or thelike.

According to an aspect of the disclosure, the abnormality may be treatedby affixing bone fasteners (such as, for example, bone screws or hooks)to one or more vertebrae and connecting the bone fasteners to a fastenerconnector (such as, for example, a rod, a curved rod, a straight rod, awire, a cross-connector rod, a cross-connector wire, or the like). Thefastener connector may be aligned with the longitudinal axis of thespinal column 2 to immobilize the spinal segment (e.g., adjacentvertebrae 4) with respect to each other. For instance, the bonefasteners may comprise bone screws that are screwed into pedicles ofvertebrae 4 and coupled to at least one fastener connector that mayinclude an elongated rod. The pedicles, which consist of a strong shellof cortical bone and a core of cancellous bone, provide the strongestpoint of attachment of a spine and, therefore, the greatest resistanceagainst bone-metal junction failure. The bone fasteners may bepositioned so as to traverse all three columns of the vertebrae, therebyproviding ventral and dorsal stability in the spinal column 2.

FIG. 2 shows an example of a bone fixation system 100 that may beimplanted in the spinal column 2 (shown in FIG. 1) of a patient's body.Once implanted in a patient's spinal column 2, the bone fixation system100 may properly position, stabilize and promote fusion in a portion ofthe spinal column 2, such as, for example, two or more adjacentvertebrae. The bone fixation system 100 may comprise any number of bonefixation devices 110 and fastener connectors 120. Each bone fixationdevice 110 may include a bone fastener assembly 200/300 and a tower 400.FIG. 2 shows one non-limiting embodiment wherein the bone fixationsystem 100 comprises three bone fixation devices 110 and a singlefastener connector 120 connecting to the bone fastener assemblies200/300 of all three of the bone fixation devices 110. The bone fastenerassembly 200/300 includes a bone fastener 200 and a coupling assembly300, collectively referred to as bone fastener assembly 200/300.According a non-limiting embodiment, the bone fastener 200 in the bonefixation device 110 may comprise a poly-axial pedicle screw 200.

FIGS. 3A to 3E show various views of the bone fixation device 110 and/orthe tower 400, according to principles of the disclosure. FIG. 3A showsa cross-section cut view of a non-limiting embodiment of the bonefixation device 110, constructed according to the principles of thedisclosure; FIG. 3B shows a top view of the bone fixation device 11 0;FIG. 3 C shows an enlarged cross-section cut view of a connectionportion A of the bone fixation device 110; FIG. 3D shows an enlargedcross-section cut view of a non-limiting embodiment of a thread pitchcompensator 350 in the bone fixation device 110; and FIG. 3E shows anexample of a receiving end of the tower 400.

Referring to FIG. 3A, the tower 400 has a tower body 410 that may beremovably attached to the coupling assembly 300. The tower body 410 mayhave a cylindrical or tube-like shape with a tool insertion channel 401formed therein by the inner walls 402 of the tower body 410. The toolinsertion channel 401 may be used to receive and guide a tool, such as,for example, a screw driver (not shown), facilitating delivery of an endof the tool (not shown) to the bone fastener 200 (for example, the headof the polyaxial pedicle screw) and/or a set screw 370, so as to allowmanipulation (e.g., tightening or loosening) of the bone fastener 200and/or the set screw 370.

As seen in FIG. 3B, when viewed from above, the walls of the tower body410 have a tower end 475 that may have a semi-closed (or semi-open)shape, such as, for example, a “C” shape having an open channel 403formed in the tower body 410. The channel 403 may be provided to allow aportion of a tool (not shown) being inserted in or through the toolinsertion channel 401 to protrude from the tower body 410, or to deployor retrieve a device such as, for example, a fastener connector 120(shown in FIG. 2) along the channel 401 using, for example, a rodinserter tool (not shown). For instance, the tool (not shown) andfastener connector 120 may be delivered along the tool insertion channel401 of the tower body 410, and when the tool end (not shown) ispositioned in a predetermined position, the fastener connector 120 maybe pivoted outward and extended from the tower body 410 (via the channel403) to be seated in or inserted into the coupling assemblies 300 in thebone fixation system 100 (shown in FIG. 2). The walls of the tower body410 may include one or more openings (or cutouts) 412 that may run alongless than the entire length of the tower 400. Alternatively, the opening(or cutout) may run along the entire length of the tower 400.

Alternatively, the tower body 410 may be a closed type (not shown) thathas a closed loop all around, or an open type (not shown) that may havemultiple open channels (or cutouts) 403 formed on opposite sides of thetower 400. The tower body 410 may include openings (or cutouts) 412,which may run along the entire length of the tower 400. Alternatively,the openings (or cutouts) 412 may run along less than the entire lengthof the tower 400. The length of one opening (or cutout) 412 may be thesame as, or differ from the length of the other opening (or cutout) 412.

As seen in FIG. 3C, the coupling assembly 300 may include a couplingbody (or unit) 310 and a set screw 370. The coupling assembly 300 mayfurther include a first (or upper) inner ring 380 and a second (orlower) inner ring 390. The coupling body 310 may have a tulip-shape, ora “U”-shape at a first (or upper) end, so as to allow the fastenerconnector 120 (shown in FIG. 2) to be positioned within a channel 302,which may be formed by upper inner walls of the coupling body 310. Thewidth of the channel 302 may be substantially the same as, or greaterthan the width (or diameter) of the fastener connector 120.

The coupling body 310 may have a cavity at its opposite (or lower) end.The cavity may be formed by the inner walls of the lower portion of thecoupling body 310. The coupling body 310 may further include a stopagainst which a portion of the upper surface of the upper inner ring 380may rest. The coupling body 310 may further include a lip portion 312that may protrude inward and serve as a stop to limit downward movementof the lower inner ring 390 from the cavity. The cavity may beconfigured to receive and hold the first (upper) inner ring 380 and thesecond (lower) inner ring 390, partially or entirely within the cavity.

In the embodiment where the bone fastener 200 includes a polyaxialpedicle screw, when assembled the first inner ring 380 and second innerring 390 may form a further cavity that holds a head portion 210 of thepolyaxial pedicle screw. The first inner ring 380 and the second innerring 390 are designed such that when a force is applied in the directionof the arrow 10 (e.g., a force that is substantially perpendicular tothe plane of the upper surface of the inner ring 380), the volume of thecavity that holds the head portion 210 of the bone fastener 200 iscompressed or reduced, thereby securely engaging and holding the headportion 210 of the bone fastener 200 by the inner walls of the firstinner ring 380 and/or second inner ring 390. In the example shown inFIG. 3C, the force is applied to the upper surface of the inner ring 380by the fastener connector 120 (shown in FIG. 2), which may be forced tomove in the direction of the arrow 10 by the set screw 370, as the setscrew 370 is turned and driven toward the first inner ring 380. Thedesign of the coupling assembly 300 is configured such that the upperinner ring 380 may transfer load from the fastener connector 120 to thetop surface of the head portion 210 of the bone fastener 200. The designupgrades line contact into surface contact for stable seating of thefastener connector 120 and load transfer.

Referring to FIG. 3C and FIG. 3D, the bone fixation device 110 mayinclude a thread pitch mismatch compensator 350. As seen in FIG. 3D,according to a non-limiting embodiment, the thread pitch mismatchcompensator 350 includes a coupling guide 420 that receives and guides acoupling lip 355 of the coupling body 310. The coupling guide 420 may beconfigured to receive and guide known coupling body housings, so thatthe tower 400 may be attached to existing bone fastener assemblieshaving various sizes and configurations. The coupling guide 420 may beformed in the inner wall 402 of the tower body 410. The coupling guide420 may have an annular shape that may be cut from, or formed in asection of the inner wall 402 of the tower body 410. For instance, thecoupling guide 420 may be formed in a 360° section of the inner wall 402of the tower body 410, formed along and around the inner wall 402 of thetower body 410 and substantially perpendicular to the longitudinal axisof the tower body 410. The coupling guide 420 may be formed in less thana 360° section of the inner wall 402, or in multiple sections of theinner wall 402. The coupling guide 420 is configured to receive, hold,and guide a coupling lip 355 on the coupling body 310, allowing thecoupling lip 355 to travel in the coupling guide 420 in either directionalong the longitudinal axis of the tower body 410.

The coupling guide 420 may include a stop 424 and a tower lip 421 thatmay function to limit the travel of the coupling lip 355 at each end ofthe coupling guide 420. The stop 424 may include a wall surface that issubstantially perpendicular to the longitudinal axis of the tower body410. The tower lip 421 may include a first wall 426 that has a surfacethat is substantially perpendicular to the longitudinal axis of thetower body 410 and faces the coupling guide 420. The tower lip 421 mayinclude a second wall 428 that may have an angled or tapered surface.The surface angle of the wall 428 may be, for example, between 5° and90° with respect to the longitudinal axis of the tower body 410, andpreferably between 30° and 60°. The surface angle of the wall 428 may beless than 5°, or more than 90° with respect to the longitudinal axis ofthe tower body 410. The surface of the wall 428 may be angled or taperedto allow the coupling lip 355 of the coupling body 310 to be forced by,and guided along the angled surface of the wall 428, past an edge of thewall 426, and allowed to be snapped into position in the coupling guide420.

The tower lip 421 may be annular shaped and may be formed 360° aroundthe inner wall 402 of the tower body 410. Alternatively, the tower lip421 may be less than 360° and may be formed along one or more portionsof the inner wall 402 of the tower body 410.

The upper portion of the coupling body 310, including the coupling lip355, may be configured to be compressible, thereby allowing theperimeter of the coupling lip 355 to be reduced upon application of anexternal inward force (e.g., a force applied in the direction of thecenter of the coupling lip 355 by the surface of the wall 428), and toexpand to a default configuration in the absence of an external force(shown in FIG. 3C).

Alternatively (or additionally), the bone fastener receiving end of thetower 400 (portion A, shown in FIG. 3A) may be made of a material thatmay flex (or stretch) satisfactorily under force and revert to a defaultconfiguration (shown in FIG. 3C) after the force is removed. The forcemay be introduced by the outer surfaces of the coupling lip 355 when thecoupling lip 355 is inserted into the coupling guide 420.

FIG. 3E shows an example of a bone fastener assembly receiving end ofthe tower 400 having a tower lip 421 formed as a pair of tower lipsegments 421′. As seen, the tower lip segments 421′ may be positionedopposite each, with spaces 425 being left open therebetween. The lengthsof the tower lip segments 421′ may be the same, or one tower lip segment421′ may be longer than the other. The lengths of the spaces 425 may besubstantial identical or different.

According to a non-limiting embodiment of the tower 400, the lengths ofthe tower lip segments 421′ may be substantially the same as, or lessthan the width of the channel 302 in the coupling body 310. In thisembodiment, the coupling lip 355 may be formed as a pair of coupling lipsegments provided on each of the pair of upper portions of the couplingbody 310 that form the U-shape and channel 302 therebetween. Duringassembly, the pair of coupling lip segments provided on the pair ofupper portions of the coupling 310 may be aligned with the spaces 425and the coupling body 310 inserted into the tower end (shown in FIG. 3E)until upper surfaces of the coupling lip 355 contact (or nearly contact)the stop 424 of the coupling guide 420. Then, the tower body 421 (and/orcoupling body 310) may be rotated until the coupling lip segmentssubstantially overlap with the tower lip segments 421′, thereby securingthe coupling lip 355 in the coupling guide 420.

According to a further non-limiting embodiment of the tower 400, thetower lip 421 may be configure as a single 360° thread (not shown) thatmay allow the coupling lip 355 to be inserted in and guided by thethread into the coupling guide 420 when the coupling body 310 (or towerbody 410) is rotated at least one complete turn with respect to thetower body 410 (or coupling body 310). The thread maybe less than 360°or greater than 360°.

The coupling body 310 may include one or more recessed grooves 356. Thegroove 356 may be formed in the outer wall 311 of the coupling body 310.The groove 356 may have a substantially flat, an annular, or asemi-annular shape that may be cut from, or formed in the coupling body310. In a non-limiting embodiment of the coupling body 310 having tulip(or U-shaped) upper portions, at least one groove 356 may be provide inthe outer wall 311 of each upper portion near the coupling lip segmentthat is provided at upper end of the coupling body 310.

According to another non-limiting embodiment of the coupling body 310,the groove 356 may be formed in a 360° section of the outerwall 311,formed along and around the entire perimeter of the outer wall 311. Thegroove 356 may be formed substantially perpendicular to the longitudinalaxis of the coupling body 310 and/or the tower body 410. The groove 356may be formed in less than a 360° section of the outer wall 311, asdiscussed herein with respect to the embodiment shown in FIG. 3E. Thegroove 356 may be configured to receive, hold, and guide the tower lip421 (or tower lip segment 421′), allowing the tower lip 421 to travel ineither direction in the groove 356, along the longitudinal axis of thecoupling body 310 and/or tower body 410. The tower lip 421 may also bepermitted to travel in and along the groove 356 in a direction that issubstantially perpendicular to the longitudinal axis of the couplingbody 310, such as, for example, when the coupling body 310 is rotatedwith respect to the tower body 410.

The groove 356 may include one or more walls 357, 358. The walls 357and/or 358 may function to limit travel of the tower lip 421 in thegroove 356 along the longitudinal axis of the tower body 410. Accordingto a non-limiting embodiment, the wall 358 may be a portion of thecoupling lip 355, the surface of which may be formed to face the groove356 and be substantially perpendicular to the longitudinal axis of thecoupling body 310. The wall 357 includes a surface that may besubstantially perpendicular to the longitudinal axis of the tower body421 and facing the groove 356.

FIGS. 4A, 4B and 4C show three enlarged cross-sectional cut views of thethread pitch mismatch compensator 350 at three different stages ofimplementation to compensate the thread pitch mismatch and misalignmentthat may otherwise occur between the threads 319, 419 of the couplingassembly 300 and the tower 400, respectively.

FIG. 4A shows an example of a stage of implementation of the threadpitch mismatch compensator 350, wherein thread misalignment and threadpitch mismatch between the inner surfaces of the coupling body 310 andthe tower 400. It is understood that, without the thread pitch mismatchcompensator 350, the configuration in FIG. 4A would block any furtherdownward movement of the set screw 370. However, the thread mismatchcompensator 350 compensates for the thread pitch mismatch by allowingthe coupling body 310 to move with respect to the tower body 410 (shownin FIGS. 4A-4C) until such time as the threads 319 of the coupling body310 are matched to the threads 379 of the set screw 370, allowing theset screw to engage and progress along the threads 319 of the couplingbody 310.

As seen in FIG. 4B, with the coupling guide 420 that allows movement ofthe coupling body 310 with respect to the tower body 410, when arotational force is applied to move the set screw 370 further downward,the coupling body 310 may be pushed and move downward by the set screw370. The coupling lip 355 may contact the surface wall of the couplingguide 420 and be guided along the coupling guide 420, such that thethreaded inner surface of the coupling body 310 does not move laterallywhen the coupling body 310 is pushed down by the set screw 370. Thecoupling body 310 may be further guided by the contact 429 between theouter wall 311 and the inner wall 402 of the tower body. The couplingbody 310 may continue to move until the threads 379 on the set screw 370are aligned with and match the threads 319 in the coupling body 310(shown in FIG. 4B). After the threads 379 and 319 match, the set screw370 may engage and proceed along the thread 319 and, thereby, innerwalls of the coupling body 310.

As seen in FIG. 4C, at some point of the rotational and downwardmovement of set screw 370, the thread pitch of the threads 379 and 319,as well as the thread pitch of the threads 419 in the tower 400, becomealigned and the set screw 370 may begin to mate with the thread 319 ofthe coupling body 310. The set screw 370 may then make a transition fromthe tower body 410 and into the coupling body 310.

Accordingly, the bone fixation device 110 may be constructed tocompensate the thread pitch mismatch between the threads of the couplingassembly 300 and the tower 400, which can eliminate cross threadingtherebetween. No additional parts are required to implement the threadpitch mismatch compensation features, and, therefore, the size andnumber of moving parts of the bone fixation device 110 may be minimized,thereby facilitating minimally invasive surgery (MIS) procedures. Also,the same tower 400 may be interchangeably used with bone fastenerassemblies 200/300 having different sizes and/or configurations to formthe bone fixation device 110.

A method of implanting the bone fixation system 100 (shown in FIG. 2),and more particularly, a plurality of bone fixation devices 110 andfastener connectors 120 will now be described. Initially, the patientmay be placed in a prone position on a radiolucent table and draped inthe usual manner. Using imaging, such as, for example, fluoroscopy andpreoperative imaging, a location may be determined for each incision andthe incision made. After the necessary incision is made, a targetingneedle (not shown) may be inserted through the dissected tissue to thelevel of a target pedicle. After confirming that the targeting needle isproperly placed and has the correct trajectory, the targeting needle maybe tapped into the vertebral body until depth is satisfactory. Thetrajectory and depth of the targeting needle should be repeatedlyconfirmed using the imaging (e.g., fluoroscopy) as the needle is beinginserted.

After the needle is inserted to its final position, an inner stylus (notshown) may be removed from the needle and a K-wire inserted in its placeto an appropriate depth. The targeting needle may then be removed whilecarefully maintaining control of the depth of the guide wire. Theforegoing steps may be repeated for each of the remaining pedicles.

Next, a dilator (not shown) may be inserted over the guide wire, keepingthe guide wire steady in the process. Once properly placed, the starterdilator tube (not shown) may be removed, leaving the second (not shown)and final dilator (not shown) in place. An appropriately sizedcannulated tap (not shown) may be inserted over the guide wire andthrough the second dilator. The cannulated tap may be tapped to desiredlength while maintaining the position and depth of the guide wire.Imaging may be used to verify that the tap is following the trajectoryof the guide wire during insertion.

At this point, the correct size and/or configuration of the bonefastener assembly 200/300 (e.g., polyaxial pedicle screw assembly) maybe selected for the particular procedure.

Referring to FIGS. 3A and 3C, after the appropriately sized bonefastener assembly 200/300 is selected for the procedure, a universaltower 400 may be attached to the bone fastener assembly 200/300 to formthe bone fixation device 110. An advantage of using a universal tower400 according to the principles of the disclosure is that only a singlesize of tower 400 could be stocked for various sizes and/orconfigurations of bone fastener assemblies 200/300 (such as, forexample, polyaxial pedicle screw assemblies). The tower 400 is bonefastener assembly-agnostic. In other words, the tower 400 may be usedwith different sizes and/or configurations of bone fastener assemblies200/300 (such as, for example, generic pedicle screw assembly housings),including bone fastener assemblies 200/300 to be used for MIS orreduction procedures.

If the bone fixation device 110 is not preassembled, it may be assembledusing the selected bone fastener assembly 200/300 with the tower 400constructed according to the principles of the disclosure.

Holding the base of the bone fastener 200 in one hand, and a portion ofthe tower body 410 at the receiving end of the tower 400 (portion A,shown in FIG. 3A) in the other hand, the bone fastener assembly 200/300may be pushed into the receiving end of the tower body 410 (portion A inFIG. 3A), such that the coupling lip 355 of the coupling body 310 isforced to compress under force of the angled wall 428 until it passes anedge of the wall 426, at which point the coupling lip 355 will be in thecoupling guide 420 and may snap to its default configuration (shown inFIG. 3C). The tower body 410 may be made of a material that may permitthe tower body 410 to flex, so as to facilitate insertion of thecoupling lip 355 past the tower lip 421 and into the coupling guide 420.In this latter regard, the coupling body 310 need not be flexible.

In at least one exemplary embodiment, such as depicted in FIGS. 8A and8B, one or more of the tower bodies 800 may incorporate one or moreflexible portions 810, which in various embodiments may comprise asection or subsection of a tower body that has been “weakened” orotherwise rendered more flexible (i.e., by machining and/or materialremoval, for example) than other portions of the tower body 800. To makethe tower housing more flexible, a series of slit cut patterns 820 orsimilar features (including other partial material removal operations)can be made along one or more regions of the tower wall structure, suchas along the middle region of the tower as shown in FIG. 8A, where acenter of curvature of the flexible section can exist. In at least oneexemplary embodiment, a desired center of curvature (or a distance fromthe rod to the center of the slit pattern) can range from 50 mm to 250mm. The tower element may be continuous, or may comprise two or more(i.e., a series) individual interlocking sections, desirably with amodular feature 830 for engaging directly with a top portion of apedicle screw housing, including attachment to a low top pedicle screwhousing in some embodiments.

As depicted in FIG. 8B, the tower bodies can include one or a pluralityof flexible portions 840, including flexible portions of differinglengths, sizes and/or positions, if desired. It some embodiments, theflexible portions can include a modular segment, which can be attachedto a desired portion of the tower at virtually any position along itslength (not shown).

During many surgical procedures, tower collision or other toolinterference can be a common occurrence due to a variety of factors,including the natural anatomy, anatomical variations between patients,injury and/or spinal degradation, and desired rod curvature and/orpedicle screw placements, which can make it difficult for a surgeon toengage subsequent instruments for compression and/or distraction. Towercollision can also be exacerbated where a curved spinal rod is used tomatch and/or correct lordotic anatomy, potentially presenting thesurgeon with a challenging rod insertion and/or alignment as well assignificantly limiting the amount of “real estate” available toaccommodate additional surgical instrumentation. In addition, towercollision and/or interference (see FIG. 9A) can inhibit proper screwplacement and/or cause “false” set screw tightening (see gap 900 of FIG.9C), where the construct may be misaligned and cause the set screw tocross-thread and/or prematurely lock. Such occurrence can eventuallyresult in loosening and/or failure of the spinal construct during spinalmotion and/or the patient's healing process.

By incorporating a flexible element in the tower that is can be capableof significant flexion (up to 360 degrees about the longitudinal axis ofthe tower in some embodiments), the present invention can allow proximalportions of the tower to be displaced in a desired direction and/ororientation while the remaining distal portion(s) of the tower can beattached and/or remain connected to the fixation screw in a desiredmanner. This arrangement desirably prevents and/or reduces theopportunity for collision and/or interference between adjacent towers,which often occurs when patient concavity of the spine is steep (i.e.,small radius), making the tall tower exceed the radius of the curvatureof the spine. As shown in FIG. 9B, once the fixation elements have beenimplanted into the spine, upon tightening the set screw the housingdesirably becomes normal (i.e., perpendicular) to the rod, with thescrew immovably fixed to the housing. However, where tower collisionand/or interference occurs, in some cases this interference creates aforce F (represented by sideways arrows in FIG. 9C) that inhibits and/orprevents the housing from assuming a normal orientation, allowing a gap900 or other space to exist between portions of the fixation rod 910 andthe set screw 920 during screw tightening, which can allow the set screwto loosen and/or other construct to fail after tower removal and/orduring patient movement.

In at least one exemplary embodiment, the tower housing can be renderedflexible in one or more regions by forming slit cut patterns or anyother form of material removal, which on one exemplary embodiment can bemade along the tower's middle region near where the center of thecurvature meets. This creation of a flexible zone can be integrated intoany percutaneous pedicle screws with high towers or it would apply toany modular reduction tower or similar element (see FIGS. 10A and 10B).

FIGS. 11A and 11B depict an alternative embodiment of rigidity reducingcuts 1100 provided on upstanding leg portions 1110 of a minimallyinvasive screw assembly 1120. In this embodiment, portions of theassembly 1120 can be flexed in a desired direction while continuing toprovide an access path through the patient's tissues in a desiredmanner. In various alternative embodiments, the flexible section couldcomprise a section of weaker material, such as a different and/or softermaterial that the remainder of the assembly, or the flexible sectioncould comprise a portion of reduced cross-section or different design ofthe same material that potentially leads to an increased flexibilityand/or greater ductility.

FIGS. 12A through 12C and 13A through 13F depict additional alternativeembodiments of flexible regions that can be formed in various spinalinstrumentation. If desired, the flexible region can be designed toprovide a full 360 degrees of flexion about the longitudinal axis of thetool, while other embodiments might provide flexion along only one ormore axis, while inhibiting flexion along other axes. In addition, theflexion slits may completely encircle the too, or may be provided onlyabout a portion of the circumference of the tool, such as less than 180degrees and/or less than 90 degrees and/or less than 45 degrees of thecircumference of the tool.

In various of the described non-limiting embodiments of a tower 400having a tower lip 421 that comprises multiple tower lip segments 421′(shown in FIG. 3E), the bone fixation device 110 may be assembled byholding the base of the bone fastener 200 in one hand, and a portion ofthe tower body 410 at the receiving end of the tower 400 (portion A,shown in FIG. 3A) in the other hand, aligning the coupling lip segmentsof the coupling body 310 with the spaces 425 in the tower 400, pushingthe coupling body 310 into the receiving end of the tower body 410(portion A in FIG. 3A) and past the tower lip segments 421′, and, whenproperly inserted, turning one or both of the tower body 410 andcoupling body 310 with respect to each until the coupling lip segmentssubstantially overlap with the tower lip segments 421′.

Once the tower 400 and bone fastener assembly 200/300 are properlyassembled, such as, for example, when the channel(s) 403 (if any) of thetower body 410 is aligned with the channel 302 in the coupling body 310,a cannulated bone screw driver assembly (not shown) may be inserted inthe tool channel 401. The screw driver (not shown) may be insertedthrough the tool channel 401 to the head of the bone fastener 200, atwhich point the screw driver (not shown) may be manipulated to properlyseat the male (or female) end of the head of the screw driver (notshown) in the female (or male) end of the bone fastener 200. Once thescrew driver head (not shown) is properly seated, an outer sleeve (notshown) of the screw driver may be rotated to tighten the screw driverwith respect to the tower body 410. The cannulated bone fastener 200 maythen be placed over the guide K-wire and slid through the final dilatorto the pedicle. Once the bone fastener 200 reaches the vertebral body,the guide wire may be removed and the bone fastener 200 advanced to thedesired depth by rotating the screw driver (not shown). The cannulatedscrew driver (not shown) and the final dilator may be removed at thispoint.

The above process may be repeated for each of the target pedicles.

After two or more of the bone fastener devices 110 have been installed,as described above, rod measurement calipers (not shown) may be used asis known in the art. The towers 400 in the bone fixation system (e.g.,shown in FIG. 2) may be aligned such that the channels 302 of thecoupling assemblies 300 are aligned. Also, the open channel(s) 403and/or slots 412 may be aligned. Then, the appropriate fastenerconnector 120 may be selected together with an appropriate inserter tool(not shown, such as, e.g., an offset left rod inserter, an offset rightrod inserter, an in-line rod inserter, or the like). The inserter tool(not shown) may be inserted in and guided through the tool channel 401to a predetermined position in the tower body, at which point thefastener connector 120 may be deployed and placed in the channel 302 ofeach of the aligned coupling bodies 310. Alternatively, the insertertool (not shown) may be delivered to the fastener connector 120installation site(s) external to any tower 400.

If the fastener connector 120 does not fully seat in a channel 302 of acoupling body 310, standard reduction (e.g., derotation device 500(described below), standard rod pushers (not shown), supplementalreduction (e.g., using parallel reducers (not shown))), or the like maybe used to facilitate proper positioning and seating of the fastenerconnector 120 with respect to the channel 302.

After the fastener connector 120 is properly seated in each intendedcoupling body 310, then a set screw 370 may be placed on a set screwstarter tool (not shown), and the set screw starter tool (not shown)with set screw 370 may be inserted in and down the tower body 410 untilit reaches the upper surface of the coupling body 310, as seen in FIG.4A. Final tightening of the set screws 370 may be carried out by using acounter torque tube holder tool (not shown) to hold the top of the tower400, and turning the set screw tightening tool (not shown). As seen inFIG. 4B, if the pitch of the threading 379 does not match the pitch ofthe threading 319 in the coupling body, the set screw 370 will push downon the upper surface of the coupling body 310 and rotate until the pitchof the threading 379 matches that of the threading 319 in the couplingbody 310, at which point the set screw 370 will engage and progressdownward into the threading 319 in the coupling body 310 (shown in FIG.4C).

The bone fasteners 200 should be inserted with some good force andwithin the confines of the vertebra, because the pedicle should be astrong pedicle and should hold the bone fastener 200 well, since this isa fastener that is going to hold the vertebra in place while the fusionis taking place. After each bone fastener 200 is secured in place, thebone fasteners 200 may be tested by running a small current through thefasteners to determine whether the fastener may irritate a nerve. Theprocess may be repeated for each of the other fasteners.

FIG. 5 shows an example of a derotation device 500, constructedaccording to the principles of the disclosure. The derotation device 500may be used for derotation (e.g., en bloc derotation, segmentalderotation, etc.), deformity correction (e.g., rib hump correction,etc.), translation, and the like. The derotation device 500 may includea reinforced cannulated shell.

As seen in FIGS. 6A and 6B, the derotation device 500 may be configuredto slide over and at least partially encapsulate a modular derotationtower 600 (e.g., tower 400 of the bone fastening device 110 shown inFIGS. 2 and 3A). The derotation device 500 may have an elongated shapedhousing with a hollow body structure to receive the derotation tower600. The derotation device 500 may have an opening at a narrow tip end510, into which the derotation tower 600 may be inserted. The derotationdevice 500 may also include a locking mechanism, such as, for example,sliding lock 512 or the like, which may fix the tower 600 once insertedinto the derotation device 500. The derotation device 500 may alsoinclude a grip portion 520, which may have a larger diameter than thenarrow tip end 510. When manually operated with a surgeon's hand, thelarger grip portion 520 may increase the rotational torque, therebyallowing the derotation device 500 to function as a torque sleeve.

As seen in FIG. 7, a crosslink unit 700 may be used to fix two or morederotation devices 500A, 500B at a desired distance therebetween. Thecrosslink unit 700 may have an elongated body 710 having two bent ends712A, 712B. The bent ends 712A, 712B may attach to the derotationdevices 500A, 500B, respectively. For example, the body 710 may have apair of set screws 720A, 720B. As seen in FIG. 5, the derotation devices500A, 500B may include a screw hole 530 (not shown in FIG. 7) near thetop end portion thereof Referring to FIG. 7, the derotation device 500Amay be placed to contact an inner bent surface of the bent end 712A, andthen the set screw 720A may be screwed into the screw hole 530 of thederotation device 500A, which may fix the derotation device 500A to thebent end 712A of the crosslink unit 700. The derotation device 500B maybe fixed to the opposite bent end 7126 of the crosslink unit 700 in asimilar manner.

A length of the crosslink unit 700 may be adjustable. For example, thebody part 710 may be divided into two parts: first body part 710A andsecond body part 710B, which are fixed to each other by a set screw 712.To adjust the length, the set screw 712 may be unscrewed to disengagethe first and second body parts 710A, 710B from each other. Then firstand second body parts 710A, 710B may then be pulled away from each otheror pushed toward each other to increase or decrease the length of thebody 710, respectively. Once the body 710 is adjusted to a desiredlength, the set screw 712 may be screwed to fix the first and secondbody parts 710A, 710B together.

Referring to FIGS. 3A-3E, 4A-4C, 5, 6A, 6B and 7 simultaneously, thebone fixation (or stabilization) system 100, the derotation device 500,the crosslink unit 700 may be configured for use in, for example,anterior approach and discectomy applications. For instance, after apatient is positioned in a prone or supine position on, for example, aradiolucent operating table, the surgical area cleaned, incisions made,muscle tissue and/or organs moved to the side(s), and other commonsurgical procedures carried out, and the bone fixation system 100installed as described above, an individual derotation device(s) 500 (ortwo or more derotation devices 500 when connected by one or more crosslink units 700) may be manipulated by a surgeon's hand, to allow forrotational and/or axial adjustment of the derotation device(s) 500.

FIGS. 14A through 14C depict additional embodiments of tower bodies1400, 1430 and 1460 which can incorporate flexible regions 1405, 1435and 1465 as described herein. As best seen in FIGS. 14A and 14C, thetowers 1400 and 1460 can further include a single proximal bridge 1410,or a pair of proximal bridges 1470 (or various other numbers and/orlocations of bridges, including three, four or more bridges and/or pairsof bridges), which can desirably increase the strength and stability ofthe tower during use, including during alignment of the fixationelements and/or flexion of the towers.

FIGS. 15A through 15D depict one exemplary embodiment of a tower body1500 that includes a tubular body portion 1510 with an integrated tipportion 1520. If desired, the tube body 1510 can include a flexiblesection (not shown) along virtually any portion of its length, which mayinclude flexible sections at different points along each wall of thetube body, if desired. The tube body 1510 also can include one or morebridge portions 1525. In this embodiment, the integrated tip portion1520 is attached to the tube body at a reduced diameter section 1530,which desirably forms a “weakened” and/or frangible link between thetube body 1510 and the tip portion 1520. Desirably, this arrangementwill allow the tip portion 1520 to be separated from the tube body 1510at a desired point in the surgery, with the tip portion capable offunction as a polyaxial or other type head of the pedicle screwassembly.

FIGS. 16A through 16C depict another exemplary embodiment of a towerbody 1600 that includes a tubular body portion 1610 with an integratedtip portion 1620, along with a single bridge portion 1625. As similarlydescribed in combination with any of the embodiments described herein,the tube body 1610 can include a flexible section (not shown) alongvirtually any portion of its length, which may include flexible sectionsat different points along each wall of the tube body, if desired.

In various embodiments, once one or more of the individual fixationelements (i.e., the pedicle screws) are secured into the targetedanatomy in desired positions and/or orientations (which may include theplacement of connecting rods and/or set screws, one or more of the towerbodies may be removed from the tip portions. For example, FIG. 17depicts one exemplary method of removing a tubular body portion 1710from a tip portion 1720 of a tower body 1700. In this embodiment, thebridge portion 1725 of the tower body 1700 can be severed (“A”) by ametal cutter 1790 or other surgical tool, and the individual sections1740 and 1745 of the body portion 1710 can be flexed (“B”) and/orotherwise displaced, which desirably stresses, “works” and/or breaks thefrangible link 1750 (“C”), leaving the tip portion 1720 within theanatomy while allowing the individual sections 1740 and/or 1745 to beremoved. Where a flexible section (not shown) has been incorporated intothe individual sections 1740 or 1745, a tubular tool or surgical plierscan be utilized to flex a portion of the individual sections 1740 and/or1745 below the flexible section to break the frangible link in a desiredmanner.

FIGS. 18A and 18B depict front plan and cross-sectional views,respectively, of one embodiment of an exemplary fixation element 1800incorporating a tip portion 1810 which engages with a bone fastener inthe form of a polyaxial pedicle screw 1820. When fully assembled, thetip portion 1810 holds a head portion 1830 of the polyaxial pediclescrew, which can be sandwiched between a first inner ring 1840 and asecond inner ring 1850, with the inner rings designed and positionedsuch that when a force is applied in a downward direction by a set screw1890 (e.g., a force that is substantially perpendicular to the plane ofthe upper surface of the inner ring), the volume of the cavity thatholds the head portion 1830 of the bone fastener and/or a fixation rod1880 is compressed or reduced, thereby securely engaging and holding thehead portion 1830 of the bone fastener and the rod 1880 by the innerwalls of the tip portion 1810 and the rings.

FIG. 19A through 19D depict various views of a set screw 1900 for usewith various embodiments of the present invention. The set screw 1900can include a central body 1910 with externally positioned threads 1920.In various embodiments, the threads can include a sawtooth or reversethread pattern, as well as square threads and/or other thread designs todesirably reduce and/or obviate splay of the tip portion, if desired.

The terms “including,” “comprising,” and variations thereof, as used inthis disclosure, mean “including, but not limited to,” unless expresslyspecified otherwise.

The terms “a,” “an,” and “the,” as used in this disclosure, means “oneor more,” unless expressly specified otherwise.

Devices that are in communication with each other need not be incontinuous communication with each other, unless expressly specifiedotherwise. In addition, devices that are in communication with eachother may communicate directly or indirectly through one or moreintermediaries.

Although process steps, method steps, or the like, may be described in asequential order, such processes and methods may be configured to workin alternate orders. In other words, any sequence or order of steps thatmay be described does not necessarily indicate a requirement that thesteps be performed in that order. The steps of the processes or methodsdescribed herein may be performed in any order practical. Further, somesteps may be performed simultaneously.

When a single device or article is described herein, it will be readilyapparent that more than one device or article may be used in place of asingle device or article. Similarly, where more than one device orarticle is described herein, it will be readily apparent that a singledevice or article may be used in place of the more than one device orarticle. The functionality or the features of a device may bealternatively embodied by one or more other devices which are notexplicitly described as having such functionality or features.

While the disclosure has been described in terms of exemplaryembodiments, those skilled in the art will recognize that the disclosurecan be practiced with modifications in the spirit and scope of theappended claims. These examples are merely illustrative and are notmeant to be an exhaustive list of all possible designs, embodiments,applications or modifications of the disclosure.

What is claimed is:
 1. A bone fixation system, comprising: a bonefastener having a shank; a tower having at least one flexible sectionand at least one rigid section, the tower having a central openingextending longitudinally therethrough, the tower comprising a firstdetachable portion section at a first end thereof, the first detachableportion having a distal opening sized to accommodate the shank of thebone fastener, the first detachable portion having a first threadformformed on an inner surface thereof; and a set screw having an externalset screw thread configured to mate with the first threadform.
 2. Thebone fixation system of claim 1, wherein the bone fastener comprises apolyaxial pedicle screw having a head, with the shank extending from thehead.
 3. The bone fixation system of claim 1, wherein the firstdetachable portion further comprises a cavity that receives and holdsthe head of the bone fastener.
 4. The bone fixation system of claim 1,wherein the first detachable portion further comprises a channel formedby a pair of upper inner walls.
 5. The bone fixation device of claim 4,further comprising a fastener connector having a portion that seatswithin the channel.
 6. The bone fixation system of claim 1, wherein thetower further comprises a pair of elongated walls separate by at leastone channel, with at least one proximal bridge element extending overthe bridge element between the elongated walls.
 7. A bone fixationsystem, comprising: a bone fastener having an externally threaded shankand a generally spherical head; a tower having a tower body with atleast one flexible section and at least one rigid section, at least aportion of the tower body including an internal tower thread; aconnection element attached to the tower body by a frangible linkage,the connection element having a distal opening sized to accommodate theshank of the bone fastener, the connection element further having aninternal threadform formed on an inner surface therein; and a set screwhaving an external set screw thread configured to mate with the internalthreadform of the connection element.
 8. The bone fixation system ofclaim 7, wherein the bone fastener comprises a polyaxial pedicle screw,with the shank extending from the head.
 9. The bone fixation system ofclaim 7, wherein the connection element further comprises a cavity thatreceives and holds the head of the bone fastener.
 10. The bone fixationsystem of claim 7, wherein the connection element further comprises achannel formed by a pair of upper inner walls.
 11. The bone fixationdevice of claim 10, further comprising a fastener connector having aportion that seats within the channel.
 12. The bone fixation system ofclaim 1, wherein the tower further comprises a pair of elongated wallsseparate by at least one tower channel, with at least one proximalbridge element adjacent to the tower channel extending between theelongated walls.